That little panel pops out easily as anyone who has done the sticky key fix knows and as your only crack is is in that top left corner. I'd pop it out, set the broken piece back in place and tape the front to hold it in place and hit the back side with some 5 min epoxy while holding it in place. That crack will vanish... You'll see it if you look really hard because you know it's there but no one else will ever notice it.